A variety of devices, including PCs (Personal Computers) and DVD (Digital Versatile Disc) recorders, have been recently embedded with a HDD (Hard Disk Drive) for data recording. The HDDs, used for portably designed machines such as laptop PCs, are provided with a magnetic disk formed by a glass substrate with a magnetic layer disposed thereon. The HDDs are configured to record/reproduce magnetic recording information in/out of the magnetic layer using a magnetic head floated slightly above the magnetic disk face. Glass substrates have been preferably used as the substrates for the magnetic disks due to less plastically deformable characteristic thereof compared to metal substrates (e.g., aluminum substrates) and so forth.
Meanwhile, development of high-density magnetic recording has been underway for meeting the demand of increase in storage volume of HDDs. For example, the magnetic recording information area (recording bit) is minutely divided by means of a perpendicular magnetic recording method for perpendicularly directing a magnetization direction in the magnetic layer with respect to the substrate face. Accordingly, the recording volume can be increased in a single disk substrate. Further, enhancement of accuracy in information recording/reproducing (i.e., enhancement of an S/N ratio) has been underway by further protruding a recording/reproducing element of the magnetic head and thereby reducing distance between the magnetic head and the magnetic recording layer in order to further increase the storage volume. It should be noted that a control mechanism of the recording/reproducing element of the magnetic head described above is referred to as a DFH (Dynamic Flying Height) control mechanism and the magnetic head embedded with the control mechanism is referred to as a DFH head. A substrate for a magnetic disk to be used for a HDD in combination with such DFH head is fabricated to have an extremely small surface asperity for avoiding collision or contact with the magnetic head and the recording/reproducing element protruded therefrom.
Steps of fabricating a glass substrate for a magnetic disk include: a grinding step of executing grinding using fixed abrasive grains with respect to a principal face of a glass blank formed in a flat plate shape after press-molding; and a polishing step of executing polishing with respect to the principal face for removing flaws and distortion left on the principal face due to the grinding step. In the aforementioned polishing step with respect to the principal face, a method of using zirconium oxide (zirconia) abrasive grains as an abrasive has been conventionally known (Japan Patent No. 2783329).